This invention relates to display devices useful in conjunction with non-synchronous, crash type transmission gear boxes such as commonly utilized in the trucking industry. More particularly, this invention relates to a gear ratio indicator which advises the vehicle operator when to shift gears and also advises as to which gear ratio can be selected at any given moment.
For reasons of cost and fuel economy, it is common practice within the heavy trucking industry to utilize manual, "crash type", non-synchronized gear boxes for transmissions. This is preferred by trucking operators for a variety of reasons, it being noted that auomatic transmissions as utilized in automobiles present too great of an initial cost for large trucks which often times have fifteen or more different gear ratios. Similarly, synchronized type manual transmissions are also preferred in heavy-duty trucks because of the costs, complexity, and reduced reliablity in attempting to incorporate synchronous mechanisms for each of the fifteen or more gear ratios.
A continual problem during operation of such trucks equipped with a conventional, non-synchronous, multispeed transmission has been the ability to engage the transmission at the proper time and into the proper gear ratio. "Double clutching" is normally required when shifting gears in such a large transmission. More particularly, this includes depressing the clutch pedal once in order to shift the transmission to neutral and disengage the transmission input and output shafts. Then upon moving the transmission to the next gear, the clutch pedal is again depressed whenever the transmission input shaft has reached the appropriate speed in comparison to transmission output speed. Intermediate to the two clutching operations, the transmission input shaft is interconnected to the engine drive shaft so that the engine operator can determine, by experience, through sound of the engine, approximately what the transmission input shaft speed is. Simply by long experience the driver learns to compare the noises of the engine and his knowledge of his ground speed to mentally know when to complete the shift into another gear ratio, and to know what gear ratio to shift into. A traditional tachometer is also helpful to the operator, but only so long as there is no significant change in vehicle speed and normal engine operating range.
This problem becomes doubly difficult in the event that a shift is "missed", or due to traffic conditions the engine is taken out of its normal operating ranges. In such instances the vehicle speed changes sufficiently so that it becomes yet more difficult to know when to engage the transmission and to know which of up to fifteen gear ratios to select at any given moment.
Accordingly, it would be desirable to provide information to the operator precisely indicating when the ratio of transmission input speed to output speed equals a certain gear ratio available in the transmission, so that he may know precisely when to shift, and what gear ratio to shift to.